This invention relates to a paste type lead storage battery and, more particularly, to an improvement in properties of grids of a paste type lead storage battery.
Generally, grids of conventional paste type lead storage batteries are formed by casting from a lead(Pb)-antimony(Sb) alloy. A lead(Pb)-calcium(Ca) alloy having improved properties was developed to eliminate the problem of the conventional alloy relating to promotion of self discharge. Also, a method of using an expanded metal grid formed from a rolled sheet was developed apart from the casting method.
While batteries designed to be maintenance-free by adopting Pb-Ca alloy expanded metal grids have been diffused, the properties of such grids have been improved in order to reduce some drawbacks. To improve, for example, the characteristics with respect to cycles of charge and discharge including heavy discharge, a means to form a layer of Pb-Sb-arsenic(As) alloy on the surface of a grid so that degree of adhesion between the grid and the active material has been developed. To overcome the problem in that the corrosion resistance of the Pb-Ca alloy is inadequate, the provision of a layer of Pb-Sb alloy formed on the surface of the Pb-Ca alloy has been proposed, as disclosed in German Patent Laid-Open No. 2721560.
Thus, drawbacks in using the Pb-Ca alloy generally relate to the interface between the grid and the active material. Therefore means to improve this interface or methods of changing properties thereof have been studied.
The present invention is therefore intended to improve the cycle characteristics of a maintenance-free lead storage battery having Pb-Ca alloy grids with respect to heavy-load discharge and recovery after standing in a discharged state.
Because electronization of vehicles is recently being promoted, the load on the power source battery becomes larger and chances of heavy-load discharge also become increased. The period of time in which the battery is left in a discharged state, as well as the frequency of standing in such a state, is thereby increased. It is therefore important to assure the desired performance of starting after standing in a discharged state.
In the case of an agricultural machine, the battery is periodically used in such a manner that it is left for a long period of time after being used, because the term of operation of the machine is limited. When the battery is used again after being left in a discharged state, it is possible that the battery cannot be changed smoothly. To cope with this problem, a layer having a large content of Sn may be formed on the surface of the grid. However, during repetition of standing in a discharged state, restoration of the desired performance becomes difficult. In particular, a reduction in high- rate-discharge performance after standing is considerable.